Method of lowering the iron content of chromite ores or concentrates without appreciable lowering of the contained cr2o3



U ed at P e This invention relates to the mineral known as chromite,

.-.in any ores or concentrates, of any degree of fineness, that aretermed chromite and that consist essentially of the oxides of chromium,iron, magnesium and aluminum in variable proportions, and has for itsobject an improved method for the extraction of part of the iron fromthe chromite mineral without appreciable lowering of the chromitecontent, thus in effect, raising the chromium: iron ratio to a higherfactor than the ratio originally present.

The usual chemical formula used for chromite is FeO.Cr O and purechromite should theoretically contain 68% chromic oxide and 32% ferrousoxide. Pure chromite is not found in nature, since in all naturaldeposits part of the chromium and part of the iron has been replaced byaluminum and magnesium. For metallurgical grade chromite, a chromitematerial containing a minimum of about 45% Cr O is required, and achromium: iron ratio of at least 3:1 is a requisite. Metallurgical gradechromite of this character is the type required for the fabrication ofalloys of chromium. The most highly industrialized countries have nocommercial deposits of this grade. There are many deposits in manycountries, wherein the chromiumriron ratio is 2:1 or 2.5 :1, and whereinthe chromium content after mechanical concentration would besufliciently high if a part of the iron could be removed withoutlowering the chromium content. Work in the past, to the bmt of myknowledge, has been devoted chiefly to attempts to leach out part of theiron by very fine grinding followed by leaching under pressure, at hightemperatures for long periods of time with strong, expensive solvents.The costs of treatment by such methods have precluded favorable economicresults, and the loss of chromite invariably experienced has not onlymeant a further charge against such processes but has also partlynullified the improvement in the chromiumziron ratio otherwiseresultant. In my improved process for raising the chromiumfirbn ratio, Ican make it possible to lower the iron to any economically desirablepoint without loss of more than 1% of the chromium content, usingrelatively small quantities of inexpensive reagents availableeverywhere, and since the iron leaching is done at air temperature, atatmospheric pressure, and in a few minutes time, the process can becontinuous rather than a batch operation. Since chromium losses in myprocess are negligible, the total degree of iron removal accrues to thebenefit of the improved chromiumziron ratio, and since the chromium,aluminum, and magnesium oxides are relatively unaffected in the process,all reagents consumed are almost 100% eflicient as regards iron removal.

The formula for chromite is'usually accepted to be FeO.Cr O The dotbetween the ferrous oxide compo nent-and the chromic oxide componentindicates that there are two radicals present (a radical being a groupof atoms which behave as an entity) which are somewhat looselyconnected. FeO is usually soluble in common reagent acids withoutdifiiculty, but since chromite can be ground very fine and agitated forlong periods in varying strengths of sulphuric acid without appreciabledecomposition or without solution of appreciable quantities of iron, theFeO is evidently protected in chromite by the Cr O radical. The FeO alsoappears to be protected against reduction since intense heating ofchromite in a reducing atmosphere renders it only slightly more magneticand only slightly more susceptible to attack by sulphuric acid of anystrength. On the other hand, the FeO does not appear to have as muchprotection against oxidation, since samples of chromite of 10 mesh sizewhich have been wetted and subsequently dried slowly turn from shinyblack to dull brown. Such accidentally air-oxidized chromite can becaused to become noticeably magnetic by heating to redness in a reducingatmosphere.

I have found that chromite ores of any grade and of any chromiumzironratio can be thoroughly oxidized by roasting at approximately 700 C.with access of air and constant rabbling. The time required for thoroughoxidation depends upon the accessability of air, the efficiency ofrabbling, and the maximum particle size. Onefourth inch material can beoxidized but I prefer to use minus 10 mesh chromite, sinceminus 10 meshmaterial gives me more rapid oxidation than coarser sizes, and lessdusting than does finer sizes. With good air supply and good rabbling,on a thin bed, 30 minutes is suflicient time for oxidation, but inmaking tests with hand rabbling I prefer to use a three-hour oxidizingperiod when plotting variables other than length-of-oxidation period.

Since we start with FeO.Cr O= and oxidize at 700 C., I theorize theiron, after oxidation, must be in the form of Fe O This conclusion isfortified by the fact that the oxidized product is nonmagnetic, is onlyvery slightly attacked by sulphuric acid at any strength, and shows theslight increase in weight necessary to support such assumption. Sincethere are now two atoms of iron in the Fe radical, the formula for theoxidized chromite must be written Fe O .2Cr O as the chromium to ironproportions have not been changed. I prefer to show the new arrangementthusly,

OrzOs The oxidation reaction formula is4(FeO.Cr O plus 0 equals 2Fe O.4Cr O I have found that the iron in the oxidized product can be readilypreferentially reduced by exposure to a reducing atmosphere such as onehigh in carbon monoxide or hydrogenat a temperature of approximately1200 C. For laboratory tests, I prefer to mix the minus 10 mesh oxidizedproduct with about 15% of its own Weight of minus 10 mesh ordinarylow-grade bituminous coal and reduce the charge for four hours at1200-1260" C. in S-O-gram fireclay crucibles. Usingv 15% coal meanstheoretically a great excess, but the 30-gram crucibles are only aboutsix inches tall, consequently much 00 1 8 expelled into the atmosphere.The efficiency of the reducing agent is dependent upon the opportunityit has for contact, therefore a long and narrow tube is much moreeflicient. I have obtained an equal amount of reduction with much lesscoal when working with a fire-clay tube three inches in inside diameterby eighteen inches long. I have also attained very satisfactoryreduction in iron pipes, one inch by fifteen inches long and threeinches diameter by fifteen inches long. The iron pipe does not enterinto any reaction and does not corrode on the inside but sooncrystallizes and breaks up from the outside because of the direct heat.In a large'scale installation, reduction should be satisfactorilyachieved in a rotary kiln and possibly in a roaster of the CFluo-Solidstypefor sizes fine enough for iluidizaiton. If a kiln were used, thereducing agent could not be gained from coal fed in with the ore, butwould have to be fed as a gas into the discharge end of the kiln so asto travel counter-currently 3, to the chromite flow. An advantage ofusing a rotary kiln which could be realized also with certain othertypes of apparatus, lies in the fact that the hot exhaust gases from thekiln can be used as the source of heat for the prior oxidation reaction,and the hot oxidized chromite can be charged directly into the reducingapparatus without substantial loss of heat. When coal or otherhydrocarbons are used as the source of the reducing agent, and thereduction is performed in a tube-shaped vessel with at least one endhaving an aperture open so that there is no build-up in pressure, theiron in the chromite is preferentially reduced, in part, to anacid-soluble form. Such reduction takes place, to some extent, at alltemperatures between 500 deg, C. and the fusing temperature of chromite(about 1500 deg. C.) but reductions at low temperature is slow andsuperficial. I prefer to use reducing temperatures of 1200-l260 deg. C.on minus 10 mesh material when using coal or other hydrocarbons, as thesource of the reducing agent, in a relatively long, narrow vessel for aperiod of four hours total reduction time. i The formula cfor thereduction stage can be writt-en- '3Fe O .6Cr O plus 2C0 equals Fe O plus3FeO.6Cr O plus 200 I prefer to show the reactions in a manner thatbetter demonstrates the reasons why re-arrangement of the chromitemolecule is possible. In FeO.Cr O any reduction of the ferrous radicalcan only result in the formation of metallic Fe. To change the iron to areadily soluble form requires oxidation to Fe O This cannot be donedirectly because direct oxidation results in the highest common state ofoxidation, Fe O When the iron is oxidized to Fe O there must necessarilybe two Cr O radicals to each one Fe O radical to make the number ofatoms present of each be in balance. Instead of writing the formula asFe O 2Or O I prefer to show i as V FezOaCmOa CrzOa Thus, while onechromium-bearing radical ordinarily protects its respective iron-bearingradical from attack, we now have a new molecular arrangement in whichtwo chromium-bearing radicals are satisfied with sharing one ironbearing radical. Then, when the iron-hearing radical is reduced to alower state of oxidation, only half of the iron is retained as FeO tosatisfy the newly-acquired requirements of the molecule for a one-ironradical:twochromium radicals ratio. The entire set of equations may bewritten in balanced form as-- In oxidation 12(F60-CI'203) plus 30 equals6F6203.12Cl'203 or to show the molecular arrangement I Then thereduction reaction can be shown as 6(FezOa.CrsOx) plus 400 equals 2Fe O4plus 6(FeO.Cr2O3) plus 460,

Cl'zOa CrsOa in which each FeO radical is sufiicient to satisfy two Cr Oradicals, the possibility of which is proved by the fact that the ironcan be caused to go into a state of oxidation higher than the originalFeO. I have found that it is possible,-with the use of sufiicientreducing agent, to cause more drastic re-arrangement on the same systemby caus. ing one FeO radical to satisfy more than two Cr O radi cals,but when this is done, more drastic leaching procedures are necessary toextract all the available iron and recovery of chromite falls sharply.

'From chromite ore reduced in the above manner, about one-half of theoriginal iron content is readily soluble without further grinding, indilute sulphuric acid or in 4 a v sulphurous acid (a solution of S gasin water) while Cr O is attacked hardly at all, usually to the extent ofless than one percent of the contained Cr O If ferric sulphate added todilute sulphuric acid, no more iron is soluble than when dilutesulphuric acid alone is used, and the speed of iron-leaching is notincreased. I take this as evidence that little of the iron has beenreducedto metallic Fe, and the order of weight changes that take placeduring reduction further substantiate this conclusion. Since the reducedproduct is highly magnetic to; a

hand magnet, theresultant acid-soluble iron must be in the form ofmagnetite, Fe O v In most chromite ores, at the end of the reductionstep, it is, found that ten or fifteen percent of the product is not asmagnetic to a hand magnet as the balance of the product. less magnetic,proves by'assay to be lower in both iron and chromium than the bulk ofthe product, and is slight. ly less magnetic because of the differencein composition and not because of lack of reduction. Also, the chromiurnziron ratio is usually higher in this fraction than'it is in themore highly magnetic portion, which helps to compensate for the factthat the iron in the less-magnetic fraction is more resistant to thesubsequent leaching.

A sample of chromite ore of unknown origin was crushed to minus meshsize, oxidized in air with handrabbling for three hours at 750 deg. (1.,mixed with of its own weight of minus 10 mesh coal and reduced in aniron pipe three inches inside diameter by fifteen inches long which wasplugged at one end and fitted with a 3 in.

, by 1 in. hell reducer on the other end. Reduction was at I 1200 deg.C. in a .butanefired furnace for three hours.

100 grams of the reduced product was separated with a hand-magnet intograms of highly magnetic grains and 15 grams of less magnetic grains.Assays made showed the following content of the respective fractions.

Product Grams Percent Percent Orzlie Or Fe Ratio Highly magnetic 8524.98 I 12. 04 2. 07: Less magnetic 15 22. 74 8.85 2. 57:

the weight loss shown by the less magnetic product in which the ratiowas raised only to 2.78 1.

Examination of the chromiteparticles at the end of the reduction step,under the microscope, reveals numerous straight brown lines whichseemingly follow the exposed edges of parting planes, and a lessernumber of small roughly circular brownish patches. After leaching ofiron has beenaccomplished, examination of the particles under themicroscope reveals that the brownish lines and patches have disappeared,leaving open crevices and craters; This migration of iron makes thesubsequent leaching very rapid. I have found that chromite reduced inthis manner and to this condition permits approximately one-half of itsiron content to be extracted, at air temperatureand at atmosphericpressure and without any further grinding to smaller size, by leachingwith sulphuric acid of 33 /s% strength (by volume) for one hour atatmospheric pressure and temperature, by leaching with sulphuric acid of10% strength (by volume for reasonably longer periods, or :by leachingwith sulphurous acid (a solution of 6% by weight S0 gas in Water) forperiods of from 20 minutes to 4 hours, depending upon the percentage ofiron to'be removed. Sulphurous acid-of 3% strength requires a slightlylonger leaching time to be employed than when 7 iron in a shorter timethan any strength of sulphuric acid solution when both are applied atair temperature.

Grinding of reduced chromite to a finer size, as to minus This ten orfifteen percent fraction, which is 100 mesh for example, and use ofheated dilute sulphuric will hasten the leaching time to some degree,but I prefer to leach with sulphurous acid of 6% strength or nearly 6%strength at air temperature, without grinding finer than the size atwhich the chromite was reduced, for reasons of economy. With properagitation during leaching, to insure constant contact of every particlewith unsaturated leaching solution, the 20 minute leaching time is ampleto put enough iron into solution to almost double the originalchromiumziron ratio, and recovery of chrom ium in the unattacked residueis almost 100% usually well over 99%, when leaching is done withsulphurous acid at air temperature.

When dilute sulphuric acid is used with moderate heating such as at 100deg. C., but little more chromiumis dissolved. At high concentrations ofsulphuric acid applied at higher temperatures especially if done underpressure, greater amounts of chromium are lost as greater temperaturesare applied and as pressure is increased, but in my improved process,such applications of heat and pressure, with resultant losses ofchromium, are totally unnecessary. I prefer to use sulphurous acid, of6% strength, or :as nearly 6% as practical to supply, as theiron-leaching solvent, applying the solvent counter-currently to theflow of ore, .so that the fresh solvent is applied on the oldest ore andthe oldest solvent which has very little remaining S0 is on the newestore. By this means, almost 100%. of the S0 has been made available forthe solution of iron and there is no necessity for the regeneration ofthe solvent. The used-up solvent can be discarded without noxious vaporsor free acidity and with no wastage charge against it except for thewater cost. The S0 solution can be made by roasting pyrite (or othersulphides) and introducing the resultant S0 gas into water byconventional means. If the used solvent were to be regenerated with S0gas, ferric sulphate and sulphuric acid wouldbe formedby the well-knownauto-oxidation process, and since these have been shown to be inferiorto sulphurous acid for my purpose, interests of economy dictate thecounter-current flow as described with discard of used lixiviant.Theoretically, with most chromite ores, roasting of 3 tons of pyriteswill furnish enough S0 to put 100 tons of chromite into themetallurgical grade class, as far as chromiumziron ratio is concerned. 7

The primary control over the degree of potential iron extraction desiredlies in the quantity of reducing agent permitted to contact the chromiteparticles at reducing temperatures. Full'utilization of availablecarbonmonoxide'requires higher temperatures than does full utilizationof hydrogen. Very satisfactory final chromiumziron ratios can beattained on any chromite ores with'a 99% plus chromite recovery ifexcessive reduction is avoided. Optimum reduction will vary withindividual ores, but original chromiumziron ratios can be doubled in allinstances without chromite losses exceeding 1%.

A l-kilo batch of minus 10 mesh chromite of unknown derivation whichhadbeen concentrated by gravity to a product assaying 24.30% Cr and12.05% Fewith a CrzFe ratio of 2.02:1 was roasted inan electric mufflefurnace for 3 hours at approximately 700 deg. C. with'free access of airbut no appreciable draft. The charge was handrabbled during the roast.At the end of theoxidizing period, the charge was removed, cooled, andmixed with 20% of its own weight of minus 10 mesh low-grade bitu minouscoal. The mixture was poured into an iron pipe of one inch insidediameter and fourteen inches long. One end of the pipe was plugged andthe other end was left open. This charge was. heated from a coldstartto. approximately 1200 deg. C. in 30 minutes and held at ap-.proximately 1200 deg. C. for 2 /2 hours. At the end of the 3-hourreduction period the charge was quenched in water. Some coal notentirely consumed was washed out from the chromite. The chromite was allvery magnetic to a hand magnet. Half of the reduced chromite product wasground to minus 100 mesh in a hand mortar and the 6 other half was leftat minus mesh. The following leach tests were made on the reducedproducts:

calculated from chromium not found in filtrate.

RESULTS Percent Percent OrzFe Percent Leach Test Weight Gr Fe Ratio rRecovery RESULTS Percent Percent Gr: Fe Percent Leach Test Weight C'r FeRatio Cr Recovery With son. 9. 50 25. 72 7.75 3. 3211 99.26 With 1:2H2SO4 9. 55 25.65 7. 53 3. :1 99. 25

Apparently these leaches were helped =less by the pressure app-lied thanthey were hurt by the fact that no agitation could be applied. I

1 kilo of minus 10 mesh chromite of unknown origin which had beenconcentrated by gravity to a product assaying 24.30% Cr, 12.05% Fe and2.04% SiO' with a CrzFe ratio of 2.02:1 was oxidizedby roasting for 3hours at a dull red heat on an iron plate on top of a butane-firedfurnace with free access of air and constant hand-rabbling. At the endof the 3 hour oxidizing period, the charge was cooled and mixed with20'% of its own weight of minus 1 0 mesh low-grade bituminous coal. Thechromite-coal mixture was poured into a tube of refractory fire-clay 3inches in inside diameter by 14 inches long. One end of the tube wasplugged, and the other end was partially plugged with refractory cement,leaving a 1 inch opening for gas escape andsubsequent emptying. Thecharge in the tube was heated quickly-4n less than 15 minutes-4o 1260deg. C. and held at that temchromium to establish the percentage ofchromium recovery.

coal. Th1s mixture waspoured mto the 3-1nch tube and g Grams MeshSolvent Tlme 3 39 reduced in the butane furnace for four hours at 1200deg. C. At the end of the four hour reduction penod, the charge wasquenched 1n water, washed free of un- 10 -10 1 2111804 100 50 consumedcoal and timed. The reduced chromite was 50 0 6% $02---- 20 split intotwo halves, one-half pulverized to minus 100 50 1:2 H18 29 50 esh in adisc pulvcrizer, and the other half was left at g 188 28 plus 10mesh-nnnus A1 lI'lCh. for leaching tests. All tests 50 20 were performedin rolhng bottles. 50 190 1:2 20 50 100 1:2 1O 50 100 6% 0 Leach GramsMesh Solvent Time Temper- 50 100 1:2 20 Test ature, O. 10 -190 3% 20 101;5H:s0 20 grams of Fe(SO4) 25 plus 10 6% SOZ 20 111111.. 20 25 10 6%S02 replaced 20 mm. plus 20 25 plus 10 4 hours 20 with fresh S02 20 min.25 plus 10 20 111111.. 20 after 20 min. 25 plus 10 4 hours.. 20 25 -10020 111111.. e 20- 25 4hours 20 RESULTS 25 20 111111.- 20 25- 4 hours '2025 4h0urs 20 Residue Percent Percent CrzFe Percent j 25 4 hours 20 LeachTest Weight Cr Fe Ratio r 20 Reeov.

9. 39 26.13 7.47 3.50:1 99.37 RESULTS 47. 80 25. 9o 7. 90 3. 28: 1 99.68 47. 68 25. 93 7.72 3.26:1 99. 83 I 48.10 25. 79 8. 26 3.12:1 99-72 5Leach Test Weight of Percent Percent Cr:Fe 47. 96 25. 79 s. 14 3. 17:199. 71 Residue 1- Fe Ratio 9. 09 26. 41 6. 62 3. 99:1 98. 79 47.31 26.107. 35 3. 55:1 99. 82 47. 12 26. 20 7. 25 3. 61: 1 99. 63 24, 71 23. 4g9. 31 2, 52; 1 47. 36 26. 10 7. 47 3. 49:1 99. 69 41 23, 1 s, 84 2. 70:148. 66 26. 34 6. 93 3. 80:1 99.13 24.77 23. 35 9. '78 ,2. 39:1 48. 4625. 65 8. 63 2. 97:1 99. 86 24. 50 23. 64 9. 05 2. 61:1 48. 43 25. 51 s.87 2. 88:1 99. 77 24. 12 24. 25 8. 4o 2. 89:1 9.68 25.75 8.51 3. 1199.62 24,14 24 2E 8,46 2,8711 23. 95 26.14 9.01 3. :1 99. 68 24.02 24.328.48 2.87:1 23. se 26. 07 8. 24 3. 16:1 99. 65 23. 97 24. 72 8. 2. 98:19 9 is 91 0 These tests show a Cr:Fe ratlo of better than 3 :1 in allinstances except k and l in which leaching time was cut to 5 minutes.They show, that while hot 1:2 H 80 is the most effective solvent, coldleaching is as effective with S0 as 1:2 H 80 that ferric sulphate is ofno benefit, and that, while minus 10 mesh material does not leach asfast as 100 mesh, leaching of 10 mesh is satisfactorily in leachingperiods of as short as 20 minutes duration.

1 kilo of minus 10 mesh chromite of unknown origin which had beenconcentrated by gravity to a product assaying 22.87% Cr and 10.53% Fewith a chromiumziron ratio of 2.17: 1, without prior oxidation was mixedwith 20% of its own weight of minus 10 mesh low-grade bituminous coaland poured into a refractory fire-clay tube of 3 inches inside diameterby 14 inches long. One end was plugged and one end was partially pluggedleaving a 1-inch circular opening. This charge was heated to 1200 deg.C. and reduced for four hoursin a butanefired furnace. The charge wasthen quenched in water, cleaned of unconsumed coal, and dried. grams ofthe reduced chromite was leached for 20 minutes with 1:2 H 80 at 100deg. C. The leached charge was filtered, dried, weighed and assayed. Theleached residue weighed 48.81 grams, assayed 24.94% Cr and 9.18% Fewhich showed a CrzFe ratio of 2.72:1. The conclusion is that prioroxidation is necessary and probably the only reason that some change inratio was eifected here, was because of air-oxidation present in the oldsample before treatment, and/ or because of some oxidation taking placein the charge in the early stages of the intended reduction period.

A sample of chromite of unknown origin consisting of particles as largeas A inch down to 10 mesh size was screened to eliminate all plus A1inch and all minus 10 mesh. The resultant minus inch, plush 10 meshmaterial which assayed 22.87% Cr and \l0.53% Fe with a CrzFe ratio of2.17:1 was given an oxidizing roast at 700-750 deg. C. for 3 hours,hand-rabbled, on aniron plate on top of the butane-fired furnace. At theend of the 3-hour oxidation period, the change'was cooled and mixed with2 0% of its own weight in minus 10 mesh Chromium was found in leachsolutions in this series in trace amounts only. Although the alteredratios at tained here are short of the desired 3:1, the results areindicative of the surprising amount of oxidation and reduction that canbe made to occur at relatively coarse sizes.

A S-kilo sample of lump chromite marked Dr. Itens High-Grade Specimenswas crushed to minus 10 mesh size. The sample assayed'40.56% Cr and10.28%-Fe showing a CrzFe ratio of 3.95:1. 1 kilo of the minus-10 meshmaterial was given an oxidizing roast for 3 hours at 750 deg. C. on aniron plate on top of a butane-fired furnace, with constanthand-rabbling. At the end of the 3-hour oxidation period, the charge wascooled and. mixed with 16% of its own weight in minus 10 mesh low-gradecoal. This mixture was poured into two SO-gram fire-clay crucibles whichwere covered with loose-fitting porcelain covers. The charges werereduced-by heating to 1260 deg." C. for four'hours in the butane-firedfurnace. At the end i hand mortar while the other half was left at minusIO mesh for leaching tests.

Leach Test Grams Mesh Solvent Time $9 161) 10 10 30 min; 25 -10 '20minl... 20 25 -l0 20 mina 20 25 10 4 hours.... 20 10 100 25 100 20 25100 26 25. 100 20 9 10 RESULTS RESULTS OF LEACHING ON 4-HOUR REDUCTIONResidue Percent Percent Cr:Fe Percent Leeched Test Weight Cr Fe Ratio CrLeach Test Residue Percent Percent CrzFe Percent Recov. 5 Weight .Or FeRatio Cr Recov.

9.30 49.02 7.92 5.43:1 98.83 24.10 42.34 3.29 5.11:1 99.13 10 I 2:53 i;g? g: 32 2: 2% 83:2? Apparently two hours reduct1on time was notsuflic1ent under existlng cond1t1ons. 1:10 (byvolume) H 80 is aseffective as 1:2 H 80 when leaching'times of 16 hours are employed. Alsoiron extraction is almost as satis- Thls test was runmore a quahtanvespmt than to factory at 10 mesh as it is at 100 mesh when a 16-hourdetermine exact quantitative results, and these results leaching time isused 3 would be much better if the vessels used in the reducing A largesample lump chromite ore marked step had been relatively longer andnarrower than the Chromite was crushed to minus 10 mesh and concem shortsquat crucibles employed. Taking into considera- Hated by gravity to aProduct assaying 2854% Cr tion the erratics allowable in assaying, it isevident that 36% Fe and 226% sioz Showing a CrzFe ratio Sulphurous acid(a solution of 6% S02 gas in water) is 20 2.41:1. One =kilo of thisconcentrate was given an oxidizequal to or superior to much strongerconcentrations of mg roast on an iron plate on top of the butanefired mpH2504 leachmg 1S done at a1r temPeratIe l nace for 3 hours at a dull redheat, with constant handleaching time 1s confined to the short timesallowable 1n rabblingl At the end f the 34mm. oxidizing period, the acommuous Processcharge was cooled and mixed with 16% of its own weight Ala'rge P of chrmllte mark?d Lumnec of low-grade coal. The mixture waspoured into two Chmmlte was gushed to mums 10 mes]? S126 and c911 -gramfire-clay crucibles and covered with loose-fitting centrated by gravltya concentrate assaymg 28-34% porcelain covers. These were heated in thebutane furnace 12387; Fe and 240% $02, Showing a CriFe ratio of to 1260deg. C. At the end of two hours, one crucible 2.29:1. This minus 10 meshconcentrate was given an 30 was removed and its charge quenched in WaterThe OXidiZing roast for 3 hours at a dull Ted heat on an irontemperature was increased to 1370 deg. C. for the next Plate on p of thebutane-fired furnace, with constant two hours. At the end of the secondtwo-hour period, the hand-rabbling. At the end of the 3-hour oxidationperiod, second crucible was removed and its charge quenched in thecharge was cooled and mixed with 16% of its own water. The two chargeswere washed free of remaining weight of minus 10 mesh low-grade coal.This mixture unconsumed coal and then dried. Each of the two prodwaspoured into two 36-gram fire-clay crucibles and covucts was split intotwo halves, one half of which was ered with loose-fitting porcelaincovers. The two crucibles ground to minus 100 h in a hand mortar whilethe were l d i h b fi d furna d heated to other half was left at minus10 mesh for leaching tests. 1260 deg. C. One crucible was removed aftertwo hours LEACHING TESTS ON 2-HOUR REDUCTION TIME reduction time and thecharge quenched in water. The 40 other crucible was removed after fourhours reduction Leach Test Grams Mesh Solvent Leach time and its chargequenched in water. Each charge was Tlmehts Washed free of remainingunconsumed coal, dried and split 25 16 into two halves. One half of eachcharge was ground to 25 -100 16 minus 100 mesh in a hand mortar and theother half left I 58 i2 at minus 10 mesh for leaching tests.

LEACHING TESTS ON 2-HOUR REDUCTION TIME RESULTS OF LEACHING ON 2.HOURREDUCTION 5O Leach Test Grams Mesh Solvent Leach Leach Test ResiduePercent Percent CrzFe Percent Time hrs. Weight 01' Fe Ratio Cr.Recov.

Leach Test Residue Percent Percent CrzFe Percent Weight Cr e Ratio CrRecov.

LEACHING TESTS ON 4-HOUR REDUCTION TIME LEACHING TESTS 0N 4-HOURREDUCTION TIME RESULTS OF LEACHING ON 4-HOUR REDUCTION Leach Test GramsMesh Solvent Leach Leach Test Residue Percent Percent CrzFe Percent Timehrs. 7 0 Weight Cr Fe Ratio Cr.Recov.

Reduction time of two hours, under existing conditions was not enough.Four hour reduction time was sufficient, but evidently highertemperature employed (1370 deg. C.) during the latter two hours led togreater chromium losses and somewhat lesser iron solubility. I haveobserved partial fusion of chromite at temperatures of only 30 or 40degrees above the peak reached here. A temperature of 1260 deg. C.should be the upper working limit.

What is claimed is:

1. A process of upgrading chromite ore having an initial Cr:Fe ratio ofless than 3:1 to a metallurgical grade chromite ore having a final CrzFeratio of more than 3:1 wherein FeO and Cr O are molecularly bonded inboth the initial ore and in the metallurgical grade ore comprising thesteps of comminuting the ore, heating the cornminuted ore at a preferredtemperature range of about 700 to 750 centigrade under oxidizingconditions while controlling the deg-rec of comminution, the heatingtemperature and the oxidizing conditions so as to oxidize at least aportion of the FeO.Cr O therein to oxide.

References Cited in the tile or this patent, v

UNITED STATES PATENTS v I r 153,573 7 Kidwell July 28,1874 1,196,049Raus'chenplat Aug. 29, 1916 1,403,237 -Eustis Jan. 10,1922

2,123,240 Ha'mmarberg July 12, 1938 while leaving the Cr O substantiallyunchanged, and exti acting said uncombined Fe Oi with a chemical reagentreactive therewith, whereby the ratioof Or to Fe is increased.

2. .A process as set tort-h in claim 1, wherein said reduction isconducted at a preferred temperature rangejoi about 1200 to 1260 degreesoentigrade. a i

3. A process as, set forth in claim 2, wherein said reduction isconducted in an atmosphere of carbon more

1. A PROCESS OF UPGRADING CHRMITE ORE HAVING AN INITIAL CR:FE RATIO OFLESS THAN 3:1 TO A METALLURICAL GRADE CHRMITE ORE HAVING A FINAL CR:FERATIO OF MORE THAN 3:1 WHEREIN FEO AND CR2O3 ARE MOLECULARLY GRADE OREIN BOTH THE INTITIAL ORE AND IN THE METALLURGICAL RADE ORE COMPRISINGTHE STEPS OF COMMINUTING THE ORE, HEATING THE COMMINUTED ORE AT APREFERRED TEMPERATURE RANGE OF ABOUT 700* TO 750* CENTIGRADE UNDEROXIDIZING CONDITIONS WHILE CONRLLING THE DEGREE OF COMMUNITION, THEHEATING THEMPERATURE AND THE OXIDIZING CONDITIONS SO AS TO OXIDIZE ATLEAST A PORTION OF THE FEO.CR2O3 THEREIN TO FE2O3ECR2O3, REDUCING ATLEAST A PORTION OF SAID FE2O32CRO3 AT A TEMPERATURE RANGE OF ABOUT 1200*TO 1370* CENTIGRADE TO FEO.2CREO3 AND UNCOMBINED FE3O4 WHILE LEAVING THECR2O3 SUBSTANTIALLY UNCHANGED, AND EXTRACTING SAID UNOMBINED FE2O4 WITHA CHEMICAL REAGENT REACTIVE THEREWITH, WHEREBY THE RATIO OF CR TO FE ISINCREASED.